Ceria Based Nanostructures:Hydrothermal/Solvothermal Synthesis, Characterization And Catalytic Performance

Modified ceria base nanostructures have a wider application because traditional ceria faced with the serious waste of resources, the lack of precious metals and low catalytic activity of. To explore the rational design and synthesis of advanced ceria nanostructured materials with controllable morphology and diverse compositions is an important research subject, which has attracted fascinating interests in the fields of nanoscience and nanotechnology.This paper focused on controlled synthesis of ceria and ceria-based nanostructures with special morphologies, size and compositions via the hydrothermal routes. The investigations are based on three aspects:controlled synthesis, formation mechanism, and properties. The detailed information of the paper is listed as follows:1. Template-free synthesis of mesoporous-shelled CeO2hollow nanospheres and the characterization of Au-loaded ceriaMesoporous-shelled CeO2hollow nanospheres were synthesized via a hydrothermal method using CeCl3.7H2O as cerium source, hydrogen peroxide (H2O2) as oxidant and Poly(vinyl-pyrrolidone)(PVP) as coating agent. And formic acid and tert-butylamine were added into the mixture solution. Thses hollow nanospheres have narrow size distribution with an average diameter of250nm and the edge of the sphere is rough. The in situ growth mechanisms for the formation of the mesoporous-shelled ceria hollow nanospheres are proposed based on the evolutions of morphology with reaction time. This is a precipition-dissolution-renucleation-assebly and Ostwald ripening process. The freshly crystalline nanoparticles tended to self-assemble and to form loose nanospheres with the PVP-assistant, which favors the formation of the hollow structure and mesoporous shell. Both PVP and H2O2played important role in the formation of the final morphology of the products. Based on the special morphology of the as-obtained ceria, hollow structure and mesoporous shell, we chose it as the support of Au nanoparticles. It is obvious that the CeO2 mesoporous-shelled hollow nanospheres have a better catalytic activity than the solid spheres, and the loaded of Au-CeO2significantly enhances the catalytic activity of ceria.2. Zr-doped CeO2hollow slightly-truncated octahedral nanoparticles (HTONs): preparation, structure and catalytic properties toward CO oxidationNovel Ce1-xZrxO2hollow slightly-truncated octahedral nanoparticles (HTONs) have been prepared via a facile one-pot hydrothermal method with CeCl3as cerium source, ZrOCl2as dopant and PVP as assistance. In the same way, we investigated the formation mechanism through an evolution of the morphology and crystallinity with reaction time. It is believed that the possible mechanism could be described by oriented attachment and Ostwald ripening process. At first, the ceria octahedra-like nanoparticles were formed through oriented aggregation of the primary nanocrystals. The loose structures were formed. As the extension of reaction time, the Ostwald ripening is dominant and the central crystallites are evacuated to form hollow structure. Poly(vinyl-pyrrolidone)(PVP) was applied to facilitate the oriented aggregation of ceria primary nanoparticles into octahedron. And the dopant also plays a vital role in the formation of the hollow structure. By tuning the amount of ZrOCl2, to some extent, we could preliminary control the composition of dpped-CeO2nanoparticles and in the same time maintain the mophology of HTON. By contrast, the Ce1-xZrxO2HTONs exhibit high surface area, catalytic activity than the pure cera. And the Zr-doped ceria have good thermal stability.3. Fabrication of Co/Ni unitary-or binary-doped CeO2mesoporous nanospheres and Cu doped nanostructures with controllable morphologyCeria and ceria doped with transition metal ions (Co2+, Ni2+), and Co/Ni binary-doped ceria mesoporous notched hollow nanospheres were prepared from a one-step solvothermal synthesis. By introducing metal ions, the composition can be freely manipulated. The morphologies and crystalline structures of the products were characterized in detail by XRD, TEM, SEM, and HRTEM. The surface compositions of the as-prepared ceria samples were detected by Raman spectroscopy and energy-dispersive X-ray spectrometry (EDS). The surface areas and pore-size distributions of the as-obtained doped ceria mesoporous nanospheres were investigated by N2adsorption-desorption measurements. Temperature-programmed reduction measurements under H2(H2-TPR) showed the better reduction behavior of the doped ceria samples. Preliminary CO catalytic oxidation experiments indicated that the doped ceria samples showed strikingly higher catalytic activity, owing to the intrinsic surface defects of the samples. In addition, the as-obtained ceria nanospheres can be used as excellent supports for gold nanoparticles to remove CO by catalytic oxidation; therefore, they demonstrate a promising potential in environmental remediation. Furthermore, based on the above synthetic method, we changed the dopant to Cu(NO3)2to prepare the Cu-doped CeO2rod-like nanostructures. The change in morphology and size are achieved by simple adjusting of the amount of H2O and reaction temperature. The doping amount of Cu2+can be controlled by changing the initial reactants. It is believed that this one-step synthesis is a versatile approach and it could be extended to other binary or ternary metal oxide systems.4. Binary-metal doped ceria-based mesoporous nanoparticles Ce0.9-xMxZr0.1O2(M:Co, Ni, Cu):synthesis, characterization, and catalytic performanceBased on the above doped-ceria mesoporous nanospheres, we prepared the binary-doped ceria mesoporous nanosparticles (Ce0.9-xMxZr0.1O2(M:Co, Ni, Cu)) via a one-step solvothermal synthesis with ethylene glycol as solvent. The morphologies and crystalline structures of the products were characterized in detail by XRD, TEM, and HRTEM. The shape of the products can be changed to rod-like nanoparticles with the doping of Cu2+, while the shape of others are spherical nanoparticles. N2adsorption-desorption results revealed the mesoporous structures. The surface compositions of the as-prepared ceria samples were detected by Raman spectroscopy and energy-dispersive X-ray spectrometry (EDS). Because of the doping elements, the number of the oxygen vacancies has greatly increase, which highly improved the catalytic performance of the as-obtained products. The binary-doped CeO2mesoporous nanoparticles exhibited a higher catalytic properties compared to the Zr-doped CeO2particles.